Mission 44 May 23, 2010AUV Glider Bass

Failure Analysis Report

David K. Edwards

AUV Glider Pilot/Research Engineering Technologist

USF – Center for Ocean Technology

Summary of Mission and Failure Mode

Glider Bass mission 44 began with deployment approximately 200 nautical miles WNW of Egmont Key at approximately 1400 GMT on Sunday, May 23, 2010. Flight proceeded as normal thru 1000 GMT on Tuesday, May 25, 2010 when an abort occurred at a depth of approximately 180m for leak detection voltage drop below 2.0 volts.

The glider remained on the surface drifting until recovery by the R/V Weatherbird II at 1630 Thursday, May 27.

The glider was opened for inspection and root cause failure analysis. Evidence was discovered that concluded the external bladder had failed in the same manner as a previous failure that occurred ending Mission 16 in April 2009.

Failure Mode Discussion

The flight data shows leak detect voltage dropped from normal 2.5 to 2.2 during the 5am surfacing climb from the previous segment prior to the abort. The leak detection voltage threshold is 2.0v so no abort occurred immediately.

The glider surfaced, downloaded data then continued the mission. Since attitude was pitch down the water ran to the front of the flight control bay away from the leak detector. No abort was detected until the dive completed and the glider pitched up for the climb. This allowed the water to then run back and trigger the aft leak detection circuit. See Figure 1.

Minimal evidence of salt crystal formation was found on top of the aft battery pack cover running end to end. See figures 1-XXX.

Fig. 1.

Evidence of salt water on aft battery cover.

Fig. 2.

Fig. 3. Trail of salt crystals on end of battery pack and buildup in bottom of housing in front of endcap seal

Fig. 4.

Difficult to photograph. Water condensation and droplets inside the bladder exhaust tube.

Fig. 4.

Bottom view of the corrosion and salt crystals on the air pump exhaust assembly resulting in water entering the glider causing the abort.

Summary and Conclusions The failure mode was found to be a small leak in the rubber bladder itself allowing a slight escape of air at the surface followed by salt water intrusion into the bladder and then thru the air pump into the glider. A quick leak test was performed prior to removing the bladder from the glider but no leak was found with the small amount of pressure from the glider air pump.

A new design has been implemented at Teledyne Webb Research. Two revised bladders were shipped to us in previous months for installation and testing on other gliders. One is installed on Stella but has not been fully tested. The 2nd will be installed on Bass for the next deployment.

TWR is also shipping a new air pump assembly that will be installed with the new bladder assembly.